Maintain a colony of approximately 40 strains of inbred mice by strict pedigreed brother-sister matings. Breed and develop new congenic mouse strains. Make selective crosses and backcrosses between these strains. Produce antisera by immunization between these strains. Perform quality control testing by serology and skin grafting of pedigreed animals in the colony. A maximum of 3,000 mice will be maintained under this contract. All animals will be supplied by the Government. This project is a recompetition of a project presently under contract.